undertaker-scan-head: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/undertaker-scan-head - from package: undertaker

You may install the required package with command apt-get install {package}

Error in other languages:
undertaker-scan-head: bevel nie gevind nie
undertaker-scan-head: comandă negăsită
undertaker-scan-head: comando não encontrado
undertaker-scan-head: commande introuvable
undertaker-scan-head: command not found
undertaker-scan-head: käsku ei ole
undertaker-scan-head: không tìm thấy lệnh
undertaker-scan-head: komanda nerasta
undertaker-scan-head: Kommando nicht gefunden.
undertaker-scan-head: kommandot finns inte
undertaker-scan-head: komut yok
undertaker-scan-head: nie znaleziono polecenia
undertaker-scan-head: níor aimsíodh an t-ordú
undertaker-scan-head: no se encontró la orden
undertaker-scan-head: no s'ha trobat l'ordre
undertaker-scan-head: opdracht niet gevonden
undertaker-scan-head: parancs nem található
undertaker-scan-head: perintah tidak ditemukan
undertaker-scan-head: príkaz nenájdený
undertaker-scan-head: příkaz nenalezen
undertaker-scan-head: команда не найдена
undertaker-scan-head: командата не е открита
undertaker-scan-head: 命令找不到
undertaker-scan-head: コマンドが見つかりません